An energy-storage device is formed from a first and a second yarn, each yarn including a plurality of nanowires including aluminum and/or a transition metal. An anode pad is in contact with the first yarn and a cathode pad is in contact with the second yarn. Alternatively, first and second metallic electrodes may be disposed substantially in parallel, with pluralities of nanowires including aluminum and/or a transition metal extending therefrom. In another embodiment, a supercapacitor may include a niobium yarn including a plurality of niobium nanowires. Each niobium nanowire may include at least (i) a first section comprising at least one of unoxidized niobium and niobium oxide; (ii) a second section comprises a niobium pentoxide layer; and (iii) a third section comprises a layer formed by coating the niobium nanowire in at least one of a conductive polymer and a liquid metal.